Transition to exponential relaxation in weakly-disordered electron-glasses

TL;DR

This paper demonstrates that weakly-disordered electron-glasses exhibit a crossover from logarithmic to exponential relaxation, enabling the definition of a relaxation time that scales with disorder and reveals insights into the quantum metal-insulator transition.

Contribution

It introduces the observation of exponential relaxation in weakly-disordered electron-glasses and links the relaxation time to the disorder-driven metal-insulator transition.

Findings

Logarithmic relaxation crosses over to exponential relaxation.

Relaxation time t' scales with disorder near the MIT.

Electron-glass dynamics strongly depend on carrier concentration.

Abstract

The out-of-equilibrium excess conductance of electron-glasses typically relaxes with a logarithmic time-dependence. Here it is shown that the log(t) relaxation of a weakly-disordered amorphous indium-oxide films crosses-over asymptotically to an exponential dependence. This allows assigning a well-defined relaxation-time t' for a given system-disorder (characterized by the Ioffe-Regel parameter). Near the metal-insulator transition, t' obeys the scaling relation with the same critical disorder where the zero-temperature conductivity of this system vanishes. The latter defines the position of the disorder-driven metal-to-insulator transition (MIT) which is a quantum-phase-transition. In this regard the electron-glass differs from classical-glasses such as the structural-glass and spin-glass. The ability to experimentally assign an unambiguous relaxation-time allows us to demonstrate the steep dependence of the electron-glass dynamics on carrier-concentration.